The present invention relates to perpendicular magnetic recording heads, and more particularly relates to a recording head including a radial magnetic field generator which reduces unwanted noise from the soft magnetic underlayer of the recording disk.
Perpendicular magnetic recording systems have been developed for use in computer hard disk drives. A preferred approach to perpendicular magnetic recording requires the use of a magnetically soft underlayer media which provides a flux path from the trailing pole to the leading pole of the writer. The soft underlayer helps with sharp field gradients and also provides strong fields which enable writing on high coercivity media. The soft underlayer is also required during the read operation. During the read back process, the soft underlayer produces the image of magnetic charge, effectively increasing the magnetic flux coming from the media. This provides a higher signal-to-noise ratio. The magnetic anisotropy (Hk) of the soft underlayer can be tailored, typically around 50-100 Oe. This means that a field of approximately 50-100 Oe needs to be applied for the soft underlayer to saturate in the circumferential direction along the length of the recording track. The Hk of the hard magnetic recording layer is typically about 5,000-20,000 Oe.
One of the challenges of implementing perpendicular recording is to resolve the problem of soft underlayer noise. The noise is caused by domain wall motion or fringing fields generated by magnetic domains in the soft underlayer that can be sensed by the reader. For the write process to be efficient, high moment materials, e.g., Bs greater than 20 kG, may be used for the soft underlayer. If the domain distribution of such materials is not carefully controlled, very large fringing fields can introduce substantial amounts of noise in the read element. Not only can the reader sense the steady-state distribution of magnetization in the soft underlayer, but it can also affect the distribution of magnetization in the soft underlayer, thus generating time-dependent noise. Both types of noise should be minimized.
The present invention has been developed in view of the foregoing.
The present invention provides a modified perpendicular magnetic recording head which generates a relatively small magnetic field in a radial direction through the soft underlayer of a magnetic recording disk. The radial magnetic field is typically on the order of from about 5 to about 30 Oe, enough to effectively drive the magnetic domains out of the soft underlayer underneath the head. The radial magnetic field is preferably generated in the soft underlayer of the media during the read operation, and may also be generated during the write operation.
An aspect of the present invention is to provide a perpendicular magnetic recording head including at least one magnetic recording element, and means for generating a magnetic field which reduces soft magnetic underlayer noise during operation of the magnetic recording element.
Another aspect of the present invention is to provide a perpendicular magnetic recording head including at least one magnetic recording element, and a radial magnetic field generator having arms extending along opposing sides of the recording head and spaced apart from the at least one magnetic recording element.
A further aspect of the present invention is to provide a perpendicular magnetic recording system comprising a perpendicular magnetic recording disk and a perpendicular magnetic recording head. The disk includes a hard magnetic recording layer and a soft magnetic underlayer, while the perpendicular magnetic recording head includes at least one magnetic recording element and a radial magnetic field generator.
These and other aspects of the present invention will be more apparent from the following description.